Conventionally, Thomson effect, Seebeck effect and Peltier effect are known as effects relating to a thermoelectric conversion. Especially Seebeck effect is known as an effect directly converting thermal energy into electronic energy by the difference of temperature. However, Seebeck coefficient of conductors such as metals is too low to secure a necessary voltage and conductors are not practical for use. Therefore, semiconductors are developed and put to practical use.
Generally, a semiconductor using heavy metal such as bismuth telluride based material becomes mainstream.
Recently, a semiconductor using oxide and a element that provides feature for structure of semiconductor are developed.    Patent Document 1: Japanese Patent Laid-Open No. H9-092889    Patent Document 2: Japanese Patent Laid-Open No. 2001-230455    Patent Document 3: Japanese Patent Laid-Open No. 2002-078367    Patent Document 4: Japanese Patent Laid-Open No. 2002-118295    Patent Document 5: Japanese Patent Laid-Open No. 2006-019422